a) Field of the Invention
This invention relates to an optical low-pass filter to be used to remove the Moire in television cameras, electronic cameras and fiberscopes provided with a solid-state image sensor.
b) Description of the Prior Art
There is a problem that, in case an object having a geometrical pattern-shaped device is observed by using a solid-state image sensor such as CCD or an image guide or by using a combination of a solid-state image sensor and image guide, the Moire, will be generated.
Therefore, in order to solve such problem, such optical low-pass filter made of such birefringent plate as a crystal plate as is shown in FIG. 1 has been placed between an imaging lens 2 and CCD3 as shown in FIG. 2 to cut high frequency component of the image of an object with birefringence to remove the Moire.
However, there has been a problem that the optical low-pass filter made of a crystal plate or the like has a fixed crystal axis direction, therefore can not remove the Moire as required, is low in the resolving power and is large in the thickness.